1. Field of the Invention
The present invention relates to an anisotropic scattering device, and a liquid crystal display wherein back light can be effectively used.
2. Prior Art
Heretofore, the brightness of a liquid crystal panel has been reduced to half or less because the liquid crystal panel has a polarizing plate. Actually, since two polarizing plates are used on the surface and the back surface of the liquid crystal panel, the brightness of the plate has been reduced to 30 to 40% of the original brightness. In order to obtain a liquid crystal panel having higher luminance, some attempts of carrying out polarization conversion to compensate for these drawbacks have been made and are as follows.
(1) A method by means of a polarized beam splitter (hereinafter abbreviated to "PBS") (reference; ASIA DISPLAY'95, page 731);
(2) A method by means of cholesteric polarization conversion (reference; ASIA DISPLAY'95, page 735); and
(3) A method using a composite of a liquid crystal and a polymer (reference; Japanese Patent Application No. 6-208319).
However, in the aforementioned methods, the following problems arise.
(1) In the method by means of a prism, when light from a light source is parallel light, a loss is small. On the other hand, when the light has an angle, the polarization conversion efficiency is deteriorated. Therefore, an angle dependency or a wavelength dependency can cause a problem. Furthermore, since the prism is used, there arises a problem that the light weight and the compact size are insufficient.
(2) When a cholesteric film is used, there arises a problem that a cholesteric spiral pitch must have a definite distribution so as to cover the whole wavelength range, and a very complicated method for production is required.
(3) When the composite of the liquid crystal and the polymer is used, the refractive index of the composite is limited by the liquid crystal material. Consequently, there arises a problem that large anisotropic scattering cannot be obtained and, therefore, the large polarization conversion efficiency cannot be obtained. In the production, a technique such as phase separation, etc. is required so that the method becomes complicated.